Effects of fertilization at flowering stage and environmental condition during seed-filling stage on soybean seed coat cracking of different types

The effects of fertilization at the flowering stage, soil moisture and high temperature during the seed-filling stage on seed coat cracking of different types in soybean were investigated. For topdressing, calcium, silicon or NPK was applied at the flowering stage. For temperature and moisture, period from 14 September to 24 October was divided into 4 periods of 10 days in each treatments, the plants were exposed to 3-4°C higher temperature (H1-H4), dried soil (D1-D4) or wet soil (W1-W4) during each period. The cracked seeds increased in H2 and H3, meaning that the seeds are easily cracked by high temperature at R6 to R7 stages. The cracked seeds of irregular type increased in each of H2, H3 and H4 irrespective of seed size. The frequency of cracked seeds of line type was high in large seeds treated with silicon, but the seed weight was not affected by silicon treatment. The effect of dried soil on cracking was low, while W1 and W2 tended to decrease the frequency of cracked seeds and W2 decreased the cracked seeds of irregular type. It was concluded that the effects of environmental condition on cracking vary with the type of cracking, and the physiological mechanism of cracking may vary with the cracking type.